1. Field of the Invention
The present invention relates to a circuit for detecting a data segment synchronizing signal in a high-definition television (HDTV), and in particular, to a method and circuit for detecting a data segment synchronizing signal in an HDTV, which minimizes the number of gates required for the HDTV when the HDTV is realized in ASIC (i.e., Application Specific Integrated Circuit). The present invention is based on Korean Patent Application Nos. 21886/1996 and 21547/1997, which are incorporated herein by reference.
2. Description of the Related Art
Generally, in an HDTV system, a synchronizing signal is added before a signal is transmitted in a unit of a horizontal line from a TV broadcasting station. A receiver receiving the transmitted signal detects the synchronizing signal from the transmitted signal, synchronizes the transmitted signal with a horizontal line signal, and then processes the synchronized signal. The form of transmission data of a horizontal line depends on the HDTV system.
FIGS. 1 and 2 show the configurations of a data segment of U.S. Grand Alliance (GA) HDTV. One data frame consists of 626-line segments, and one segment is composed of 832 symbols which consists of 828 symbol data and four symbol data segment synchronizing signals 101, as shown in detail in FIG. 2A. One data segment corresponds to one horizontal line of the NTSC (i.e., National Television System Committee) system. The data segment synchronizing signal consists of four symbols which indicate the start of each data segment. The data segment synchronizing signal is composed in a specific pattern such that the four symbols have signal levels of +5, -5, -5 and +5, and the data segment signals have random signal levels.
Therefore, in a circuit receiving a transmission signal of the GA system, the data segment synchronizing signal is detected in the initial four-symbol period of each data segment, to thereby solve timing recovery problems and to synchronize received data segment signals. Accordingly, the detection of the data segment synchronizing signal affects the performance of the GA-VSB (i.e., Vestigial Sideband) system. An apparatus and method for generating a data segment synchronizing signal from data received are disclosed in Korean Patent Application Nos. 95-15218, 95-30746 and 96-21886.
Another general method of generating a segment synchronizing signal is explained with reference to FIG. 3. A separator 303 separates the most significant bit (hereinafter, "MSB") from eight bits of output of a filter (not shown), and uses the MSB as a reference signal. A four-symbol correlator 305 receives the MSB, and creates a symbol of location correlation between data. Since the four-symbol correlator uses only MSB as described above, 4 is output only in the case where the symbol is (+),(-),(-) and (+), and -4, -2, 0 and 2 are output in other cases. The output of the four-symbol correlator 305 is added to the output of a one-segment delay 309, that is the output from the same location as that of a preceding segment, in adder 307, and the added result is accumulated.
The output of adder 307 is sent to a maximum value detector 311. Maximum value detector 311 observes the output of the accumulated correlation symbol for 832 symbols (i.e., one segment), judges the location where the maximum value appears as a segment synchronous location, and then applies this information to a synchronizing signal generator 313. Synchronizing signal generator 313 generates a synchronizing pulse at the segment synchronous location.
As shown in FIG. 3, in the general apparatus for generating a segment synchronizing signal, because the output of the four-symbol correlator 305 is four bits, the adder and 832-symbol (i.e., one-segment) delay are required to accumulate a four-bit output. Thus, bit resolution of the apparatus is at least 8 bits. When this apparatus is realized in ASIC, an 832-symbol delay is needed, so that the apparatus requires 8bits.times.832.times.7bits gates. Accordingly, the general apparatus requires a large number of gates to perform its functions.